Which of the following law is based on the conservation of energy?

• A. Kirchhoff’s Voltage Law
• B. Kirchhoff’s Current Law
• C. Coulomb’s Law
• D. Ohm’s Law

Answer: (A)

Kirchhoff’s Voltage Law (KVL,) or Kirchhoff’s Loop Rule. This law is based on the conservation of energy and may be stated as under:
In any closed electrical circuit or loop, the algebraic sum of all the electromotive force (e.m.f s) and voltage drops in resistors is equal to zero, i.e., in any closed circuit or loop.
The algebraic sum of e.m.f s + Algebraic sum of voltage drops = 0
The validity of Kirchhoff’s voltage law can be easily established by referring to the loop ABCDA shown in Fig.
If we start from any point (say point A) in this closed circuit and go back to this point (i.e., point A) after going around the circuit, then there is no increase or decrease in potential. This means that algebraic sum of the e.m.f.s of all the sources (here only one e.m.f. source is considered) met on the way plus the algebraic sum of the voltage drops in the resistances must be zero. Kirchhoff’s voltage law is based on the law of conservation of energy, i.e., the net change in the energy of a charge alter completing the closed path is zero.
V1 + V2 − V = 0
or
Kirchhoff’s voltage law is also called as loop rule.